Highway and roadway lighting have used incandescent and more recently high intensity discharge (HID) luminaires that can provide adequate amounts of lighting, but which have several drawbacks, including frequent (at least annually) luminaire failures and uneven lighting of the traffic surface. Such lighting also disperses the light in all directions around the luminaire. Uncontrolled light can be wasted in lighting areas around the roadway that do not require lighting, and contributes to unwanted “night lighting” which can interfere with the preservation and protection of the nighttime environment and our heritage of dark skies at night.
As advances in the quality and energy efficiency of lighting sources such as LEDs have improved, their production costs have gone down. As a result, LEDs, for example are being commonly used in area lighting applications. Initial efforts to incorporating LEDs into lighting fixtures have involved retrofitting LEDs into conventional luminaries or onto or into the shape of conventional lighting luminaires.
Improvements in LED lighting technology has led to the development by Osram Sylvania of an LED having an integral optic that emits a significant portion of the LED light bilaterally and at high angle α (about 60°) from nadir, which is available as the Golden DRAGON® LED with Lens (hereinafter, “bilateral, high angular LED”). FIG. 1A is a representation of the bilateral, high angular LED 252 showing the direction and angle of the lines 255 of maximum light intensity emitted by the LED, substantially in opposed designated ±Z axes. Progressively and significantly lower levels of light intensity are emitted at angles in the Y-Z plane diverging from lines 255 and along vectors directed toward the transverse direction (±X axes) normal to the image of the figure. The radiation characteristics of the LED 252 are shown in FIG. 1B.
These LEDs can be used in a matrix arrangement in a lighting apparatus to distribute more of the light emitted from the LEDs, for example, along the length of the roadway and down both sides of the light pole. In a typical matrix, the LEDs are arranged in eighteen longitudinal rows, with five bilateral, high angular LEDs in each row. The ninety total bilateral, high angular LEDs are arranged with 36 bilateral, high angular LEDs (42%) aligned with its Z axes aligned within the housing along the longitudinal direction L, to align with the direction of the roadway; 27 bilateral, high angular LEDs (29%) aligned with its Z axes aligned +10° (toward the roadway) from the longitudinal direction L in the direction of traffic; and 27 bilateral, high angular LEDs (29%) aligned with its Z axes aligned −10° (away from the roadway) from the longitudinal direction L in the direction of traffic.
The LED lighting apparatus can be retrofitted onto existing light poles, or installed onto new light poles, for illuminating the lanes of all types of roadways, including two-way streets up to multi-lane interstate highways. As shown in FIG. 2A, the light poles are typically mounted on the sides of such roadways, typically several meters into the berm from the edge 5 of the roadway so as not to become an obstruction to traffic. Arm 4 extending from the pole 3 is configured to hold the luminaire luminaire outward toward the roadway 7. Because a large portion of the light emitted by the bilateral, high angular LEDs is directed longitudinally and in the directions (±L) that the roadway 7 runs, and since the roadway luminaire is typically mounted near the berm of the roadway 7 or only partly into the first or near lane 7n, adjustments to the luminaire must be made to ensure that emitted light is projected out into outer lanes (for example, to outer lane 7f) of the roadway. It is known to accomplish the projection of the emitted light by tilting the luminaire on an angle β from nadir to angle and disperse a significant portion of the light to the outer lane 7f or outer lanes of the roadway 7. Such angle β is typically between about 20° to about 70°, and more typically about 30°. FIG. 2B shows a simulated light distribution pattern formed by at least two conventional LED lighting apparati 18a and 18b secured to the arm of the lighting pole, positioned 30 feet (9.1 m) above the roadway and extending over the roadway four feet (1.2 m) in from the near edge 5 of the roadway, and positioned 70 feet (21 m) apart. The rectangular light distribution pattern 80 is defined by the traverse centerlines of the apparati 18a and 18b, the near edge 5, and a simulated outer edge 9 extending parallel to and 20 feet (6.1 m) laterally from the near edge 5. Each LED lighting apparati has 90 LEDs arranged in an array of 18×5 LEDs, consisting of 18 LEDs on a substrate at 1 inch (2.54 cm) spacing, with the five parallel substrates oriented in the traverse T direction, and spaced apart by about 1 inch in the longitudinal L direction. Each LED is the bilateral, high angular LED 252, as shown in FIG. 1, and is powered with 1 watt and emits 48 lumens.
While providing a significant improvement in the distribution of light along the length of the roadway, the tilting of the luminaire at high angles β from nadir also directs light toward the horizon (H), contributing to unwanted “night lighting” and creating the potential for direct light glare in the eyes of drivers and passengers in automobiles and trucks, particular those in outer lane 7f or lanes farthest from the near edge 5, including those traveling in roadway lanes with traffic moving in the opposite direction. The light directed into the horizon is wasted light resulting in wasted energy costs to power the LEDs. Tilting the luminaire is thus an inefficient manner of obtaining a proper light distribution.